Work vehicles including, but not limited to, agricultural work vehicles, such as tractors and combines, as well as construction vehicles, such as loaders and backhoes, are often supported by a set of inflatable tires. The inflation pressure of these inflatable tires can be adjusted to provide a substantially cushioned ride while providing adequate traction and support for the vehicle. Maintaining proper tire inflation provides better maneuverability and control of the work vehicle while minimizing the amount of vehicle slip, thereby increasing the amount of traction and power available for the work vehicle. Further, maintaining proper tire inflation reduces the amount of fuel necessary during operation of the work vehicle and provides improved tire wear, thereby providing substantial cost savings.
There are, however, a number of factors and conditions which cause work vehicles to be operated despite having non-optimal or improper tire inflation pressures. For example, tire inflation pressures typically decrease gradually over time due to low-level leaks and imperfect seals, and typically fluctuate as a function of temperature. In addition, the optimal tire inflation pressure will vary based upon the operating conditions of the work vehicle, such as the vehicle speed, the type of terrain, and the mission. In addition, the optimal tire inflation pressure will depend upon the operating loads placed on the tires under various operating conditions.
The traditional method of maintaining proper tire inflation pressures is to manually measure the inflation pressure of each tire and then, for each tire, to manually add air to increase pressure or to manually bleed air to decrease pressure. The effectiveness of the traditional method depends on the diligence of the operator in checking and adjusting the tire inflation pressures, and the manual method can be cumbersome due to the numerous tires found on many work vehicles. To address the drawbacks of the traditional method, central tire inflation systems operable from the operator's compartment or cab of the work vehicle have been developed for the military vehicle, commercial truck, and agricultural vehicle industries.
Existing central tire inflation systems allow the vehicle operator to view information regarding the tire inflation pressure and to manually adjust the tire inflation pressures using input devices. During operation, such existing central tire inflation systems may also maintain predetermined tire inflation pressures as set by the operator. Such existing central tire inflation systems, however, do not account for dynamic variations in the operating loads placed on the tires by weight transfers associated with implements attached to the work vehicles. The attached implements may include, for example, a mounted implement such as a plow mounted to a hitch assembly supported by an agricultural tractor, or a drawn implement such as a planter or other material spreader (e.g., a fertilizer or insecticide spreader) attached to a drawbar pulled by such a tractor. Such mounted or drawn implements exert varying loads on the tractor depending on, for example, the depth of the plow as it is being pulled through a field, or the amount of material remaining in the planter or spreader, or the condition of the surface including characteristics such as the soil type, soil moisture content, soil compaction, etc. The attached implements may also include a detachable header supported by an agricultural harvesting vehicle such as a combine or cotton picker. The load on the harvesting vehicle will vary due to the different masses and centers of gravity associated with different types of headers. In the construction vehicle field, the attached implements may include, for example, a bucket supported by a loading arm of a loader-backhoe vehicle. The load on the construction vehicle will vary not only because of the different masses and centers of gravity associated with different types of buckets or other implements, but will also vary with the amount of material (e.g., soil) being moved by the bucket.
Existing central tire inflation systems also fail to account for dynamic variations in load which occur during the operation of harvesting vehicles due to the storage of the harvested crop in containers or bins supported by the vehicle, and the unloading of the harvested crop from such bins, both of which significantly change the mass and center of gravity of the vehicle during field operations. In addition, varying vehicle speeds, terrain and missions all cause different tire inflation needs.
Thus, there is a need for a central tire inflation system that provides a manual mode wherein an operator may manually adjust the tire inflation pressures and an automatic mode wherein the pressures are automatically adjusted to account for variations in operating loads placed on the tires under various conditions. Also, there is a need for a central tire inflation system for a work vehicle which provides proper tire inflation pressures over varying combinations of load, speed, terrain and mission. There is also a need for a central tire inflation system for a work vehicle supported by inflatable tires, wherein the central tire inflation system can account for changes in tire loading due to varying loads placed on the work vehicle by attached implements, or by materials loaded into or unloaded from one or more storage bins supported by the work vehicle during operations of the work vehicle.